PHP- is unable to read the other checked checkbox - php

Question

I stored the data in a supposed to be an array but what happens is that only the last checked checkbox is the only one that is registered in the idSkills. This is the part of the code wherein the skills are displayed through a query in the database
<?php
$i=0;
while ($row = mysqli_fetch_assoc($result)) {
$id=$row['id'];
$skillName=$row['skillName'];
?>
<input type="checkbox" name="skills[]" value="<?php echo $id; ?>"><?php echo $skillName; ?><br>
<?php
$i++;
}
?>
Here is the part where the loop unveil all of the selected checkbox
//QUERY TO INSERT
$conn = new mysqli($config['servername'], $config['username'], $config['password'], $config['database']);
$idSkills = $_GET['skills'];
if(empty($idSkills))
{
echo("You didn't select any buildings.");
}
else
{
$N = count($idSkills);
echo("You selected $N door(s): ");
echo("$idSkills[1] ");
for($i=0; $i < $N; $i++) {
echo "Skill ID: "
$sql = "INSERT INTO volunteer_skills (idskill,idVolunteer)
VALUES ('$idSkills[$i]','$idVolunteer')";
$result = $conn->query($sql);
}
}
$conn->close();

Answer 1

It would be best to use a prepared statement instead of substituting a variable into the SQL. But if you're going to do it this way, you need to use the correct syntax:
$sql = "INSERT INTO volunteer_skills (idskill,idVolunteer)
VALUES ('{$idSkills[$i]}','$idVolunteer')";
You need to put {} around an array reference in order to get the variable inside the brackets to be evaluated. See the section on Complex (curly) Syntax in the PHP Strings documentation.